Production of titanium tetrachloride



niteci States PRODUCTION OF TITANIUM TETRACHLORIDE Leland R. Lyons,Boulder City, Nev., assignor to Titanium Metals Corporation of America,Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. ApplicationJanuary 25, 1954, Serial No. 406,097

4 Claims. (Cl. 23-87) perature. The briquettes may be formed of rutile,ilmenite or other titanium bearing material admixed with coke or coaland a binder such as tar or molasses. Generally the mixture is spreadout and burned to drive off volatile components and to provide a coked,porous mass which is broken up to form so called briquettes. To produceTiCl4, a bed of appreciable thickness of such briquettes is treated in afurnace at temperatures of the order of 450- 1000 C. by passing chlorinegas upwardly through the bed. The reaction produces TiCLi which is takenout of the top of the furnace as a gas and is subsequently condensed.

Serious difiiculties have arisen in the operation of such a process,however, due mainly to the character and effect of the briquettesemployed. When these are formed with a binder, such as tar, havingsuificient cohesive action to produce a coherent mixture, the mixturealso adheres strongly to the surfaces of containers and mixing devicesin which it is formed and also to the pans or surfaces on which it isfired. In addition, briquettes heretofore proposed or used havedeteriorated badly in the chlorination furnace, lacking physicalstrength and also being prone to disintegrate as the reaction withchlorine has progressed. Breaking and powdering of the briquettescreates poor furnace operating conditions either raising the backpressure against which the chlorine must be introduced to high levels,or packing in some section and allowing channels to form in others thusallowing chlorine to flow through the bed without contact with thebriquettes resulting in poor efficiency.

It is therefore the object of this invention to provide an improvedprocess for the manufacture of titanium tetrachloride. It is furtherobject of this invention to provide an improved process for themanufacture of titanium oxide containing briquettes suitable forchlorination to produce TiCl4. Another object of this invention is toprovide an improved stronger, and more uniform titanium oxide-containingbriquette adapted for chlorination to produce purer TiCl4. These andother objects of this invention will be apparent from the followingdetailed description thereof.

This invention in its broadest aspects contemplates the manufacture oftitanium tetrachloride by chlorinating at elevated temperaturebriquettes comprising a titanium xide bearing material, a carbonaceousreducing agent and a binder comprising acid treated mineral tar orpitch. In order to form the briquettes of this invention, tar or pitch,preferably coal tar, is treated with a strong mineral acid such assulphuric acid. The tar or pitch binder is admixed with comminutedtitanium oxide bearing material such as rutile or ilmenite and acarbonaceous reducing atent 1 agent such as coke or coal. The mixturemay be formed into suitable size and shape briquettes by pressing in aconventional briquetting machine for example of the type operating withpocketed rolls, referred to as Belgian rolls, and the formed briquettesare then fired. Or, alternatively, the mixture may be spread out in arelatively thin layer in pans or on a convenient surface, fired, and thefired mass broken up to make fragments of briquette size andcharacteristics.

The tar or pitch employed in the practice of this invention may be ofany type having suitable binder properties selected from those ofmineral origin which will include generally the group consisting if coaland petroleum tars and pitches. It will be appreciated that pitch ismost generally obtained by further distillation of tar, which is itselfa distillation residuum, and that these compositions differ mostly intheir viscosity characteristics and in the amount and character of theremaining oils and other volatile constituents. It is preferred however,to employ coal tar which is readily available, and a relatively thin andfluid grade should be selected to provide easy handling and good bindingproperties. The tar or pitch is treated with strong sulphuric acid bythoroughly admixing with from 2% to 25 of its weight of acid.The'temperature of the mixing operation should be such that the tar isgenerally liquid. In the case of tars which are liquid and relativelythin at normal temperatures of 15-30 C. the sulphuric acid readily formsa homogeneous product with the tar. The exact nature of the reaction isnot clearly understood but it is postulated that a chemical. and/ orphysical combination is obtained since the surface tension and cohesivequalities of the tar are noticeably changed. If the tar or pitch issolid or very viscous at room temperature or if normally liquid tar isto be treated under low ambient temperature conditions suflicient heatshould be applied to liquify the material and to obtain the properhomogeneous acid treated tar product.-

The amount of acid may vary from about 2% to about 25% by weight of thetar or pitch. Less than 2% will be found to produce little of thedesired effect and more than about 25% does not produce any appreciableadditional benefit. The rutile, carbon and acid treated tar are mixedtogether so as to produce a final composition after firing whichcontains rutile and carbon in the ratio of about 3-1 to 5-1. Therutile-carbon ratio may vary considerably but ratios less than 3-1 arenot generally advantageous. Both the rutile and the coke or coal orother reducing agent are comminuted. The degree of fineness is not ofgreat importance and in general superior results are obtained when thesematerials are not ground too fine. For the rutile or ilmenite a particlesize generally less than mesh has proved beneficial and the coal or cokeof a comparable size range will he satisfactory, although thesefinenesses may vary considerably according to specific conditions.

The amounts of carbon employed in the mixture in relation to the rutilewill be somewhat greater than the anticipated proportions in the finalfired briquette. Losses of both carbon and volatile materials occurduring firing. Therefore, it will be found that about 3 to 6 parts ofrutile or ilmenite to 1 part of coke or coal to V2 to 2 /2 parts of tarwill produce fired briquettes of the suitable composition.

The proportions of the materials are thoroughly mixed togetherpreferably by means of a mechanical mixing device such as a pug mill.The mixture is then fired by spreading out in a relatively thin layer inmetal pans and heated to a temperature high enough to ignite thevolatile constituents. After combustion is substantially complete it ispreferred to subsequently heat in the absence of air at a temperaturearound 400 to 700 C. to

Patented July 3, 1956 further reduce the volatile content. After thefinal heating the fired mass may be cooled and then broken intofragments to form briquettes. The fired material will be found to be acoherent, porous mass with substantial mechanical strength readilyadapted for chlorination. Alternatively the mixture after blending inthe pug mill may be formed into suitable size and shape briquettes bypressing on a conventional briquette machine. These briquettes may befired in the same manner as the previously described un-pressedmaterial.

As an example of the properties obtained in briquettes producedaccording to this invention compared to properties obtained inbriquettes produced employing conventional binding agents, two batchesof briquettes were made from the same original batch of rutile and coke.A mixture was prepared containing 68 parts of rutile, 16 parts coke and17 parts of tar and a second batch was prepared containing the sameamount of rutile and coke but substituting the same Weight of acidtreated tar according to this invention. The two mixes were heated in agas fired furnace to a temperature at which ignition of the volatileconstituents occurred. After all the volatiles had been burned heatingwas continued for about an hour at a temperature between 550 to 650 C.with the furnace closed to make sure that substantially all the volatilematerials had been driven off from the mixture. The pans containing thefired mixture were than taken from the furnace, allowed to cool and thelayers of the mix broken into fragments, roughly 1 inch square. Thesefinal fired briquettes were characterized, in the case of those producedusing acid treated tar, by superior mechanical strength and resistanceto disintegration during chlorination.

To test for mechanical strength, the tired briquettes were compressedbetween two plane surfaces until fracture and disintegration occurred,and the pressure measured as pounds per square inch required was takenas an indication of the briquette strength. To determine resistance todisintegration during chlorination the briquettes were treated withchlorine in a small laboratory reactor producing titanium tetrachloride.At the end of the chlorination reaction the briquettes were screened toseparate a fines portion less than 8 mesh. The percentage of theoriginal charge which had disintegrated to form fines was taken as anindication of the resistance to disintegration.

The results obtained in testing the two batches made as above are shownin Table 1 below:

It has been found additionally, that chlorination of briquettes producedaccording to this invention results in production of a purer grade oftitanium tetrachloride. Raw materials for instance, rutile or ilnienitemost generally contain a proportion of vanadium which is a harmfulimpurity in the TiCli product. Purification of titanium tetrachloride isoften necessary to eliminate vanadium compounds. In the case of TiCLiproduced from briquettes containing acid treated tar, however, the crudeTiCh produced has been found to contain substantially less vanadium thanTiCh produced by conventional and heretofore known methods. it ispostulated that the sulphur content of the briquettes when made withacid treated tar may react in some manner with vanadium to formnon-volatile or insoluble compounds. It has been found that theacceptability of TiCli, particularly for the manufacture of pigments andfor the production of titanium. metal is to a large degree dependent onits freedom from vanadium. Tests made in which briquettes according tothis invention were chlorinated, produced TiCLi having a vanadiumcontent of between .01 and .2% compared to between .3 and .5 obtainedwhen conventional briquettes of the same general composition withoutcontaining acid treated tar were employed.

The following example will illustrate a selected embodiment of thisinvention.

Example I A portion of petroleum tar having a viscosity of 19.9 SpEngler was admixed with 21% of its weight of 96% sulphuric acid. Themixture was stirred until a homogeneous product was obtained.

The acid treated tar product was admixed with rutile (minus 60 mesh) andcoke (minus 20 mesh) in the following proportions:

65 parts rutile ll parts coke 26 parts acid treated tar This mixture wasspread out in a 7 x 10 inch pan in a layer about 2 inches thick. The panand its contents were heated to ignite the volatile constituents whichburned readily for about an hour. The mixture was then heated for anadditional hour in a closed furnace in the presence of combustion gasesonly at a temperature of between 550 and 650 C. The firing operation hadconverted the mixture in the pan to a hard, coked porous layer which wasreadily removed from the pan without sticking to the sides or bottomthereof. The layer was broken into fragments of about 1 inch largestdimension to form briquettes. These briquettes were placed in a furnacemaintained at BOW-900 C. and chlorine gas passed upwardly through thebed of briquettes. Titanium tetrachloride was taken off the top of thefurnace and condcnsed to liquid in a separate condenser. At the end ofan hour and a quarter chlorination period, the chlorine was shut off andthe charge removed from the furnace. Testing of the spent briquettesshowed that only 24% of the briquettes had disintegrated to form finesof smaller than 8 mesh.

The chlorination reaction was characterized by good efficiency for thechlorine employed and low back pressure during passage of gas throughthe bed.

The titanium tetrachloride produced contained a vanadium content of 0.2%compared to a normal content of from 0.3% to as high as 0.5% for TiCl4manufacture by conventional methods from the same raw materials.

The following is an example of the practice of this invention whenemploying pressed briquettes.

Example 11 The acid treated tar product of Example I was admixed withcoke and rutile in the following proportions:

31 parts rutile 10 parts Cake 5 parts acid treated tar The mixture waspressed into l inch ovoid briquettes on a briquetting machine equippedwith Belgian rolls and the briquettes fired in the same manner as thosein Example I. After firing the briquettes showed excellent mechanicalstrength.

The fired briquettes were chlorinated to produce TiCli and afterchlorination showed 21% of fines less than 8 mesh.

While this invention has been described and illustrated by the examplesshown, it is not intended to be strictly limited thereto and othermodifications and variations may be employed within the limits of thefollowing claims.

I claim:

1. lna' process for production of titanium tetrachloride by chlorinationof briquettes containing a titanium oxide bearing material in admixturewith a carbonaceous reducing agent, the steps which comprise; treating abinder selected from the group consisting of tar and pitch with strongsulphuric acid by forming an intimate mixture consisting of said binderand said acid, in amount from 2% to 25% by weight of said binder,admixing said acid treated binder with a titanium oxide bearing materialand a carbonaceous reducing agent and forming said admixture intobriquettes adapted for chlorination.

2. In a process for production of titanium tetrachloride by chlorinationof briquettes containing a titanium oxide bearing material in admixturewith a carbonaceous reducing agent, the steps which comprise; treating abinder selected from the group consisting of tar and pitch with strongsulphuric acid by forming an intimate mixture consisting of said binderand said acid, in amount from 2% to 25% by weight of said binder,admixing said acid treated binder with a titanium oxide bearing materialand a carbonaceous reducing agent, spreading out said mixture in alayer, firing said layer by heating in air to ignite the volatileconstituents thereof and breaking said fired layer to form briquettesadapted for chlorination.

3. In a process for production of titanium tetrachloride by chlorinationof briquettes containing a titanium oxide bearing material in admixturewith a carbonaceous reducing agent, the steps which comprise; treating abinder selected from the group consisting of tar and pitch with strongsulphuric acid by forming an intimate mixture consisting of said binderand said acid, in amount from 2% to 25% by Weight of said binder,admixing said acid 30 treated binder with a titanium oxide bearingmaterial and a carbonaceous reducing agent, pressing said mixture intobriquettes and firing said briquettes by heating in air to ignite thevolatile constituents thereof and to form briquettes adapted forchlorination.

4. In a process for production of titanium tetrachloride by chlorinationof briquettes containing a titanium oxide bearing material in admixturewith a carbonaceous reducing agent, the steps which comprise; treating abinder selected from the group consisting of tar and pitch with strongsulphuric acid by forming an intimate mixture consisting of said binderand said acid, in amount from 2% to 25% by weight of said binder,admixing said acid treated binder with a titanium oxide bearing materialand a carbonaceous reducing agent, firing said mixture by heating in airto ignite the volatile constitutents thereof and subsequently heatingsaid mixture in the absence of air at a temperature of between about 400to 800 C. and forming said mixture into briquettes adapted forchlorination.

References Cited in the file of this patent UNITED STATES PATENTS1,158,366 Bibb Oct. 26, 1915 2,184,884 Muskat et al Dec. 26, 19392,560,642 Greaves et al. July 17, 1951 2,674,763 Greaves et al. Apr. 13,1954 OTHER REFERENCES Titanium, Barksdale, Ronald Press Co., N. Y. 1949,pages 317-320.

1. IN A PROCESS FOR PRODUCTION OF TITAMIUM TETRACHLORIDE BY CHLORINATIONOF BRIQUETTES CONTAINING A TITANIUM OXIDE BEARING MATERIAL IN ADMIXTUREWITH A CARBONACEOUS REDUCING AGENT, THE STEPS WHICH COMPRISE; TREATING ABINDER SELECTED FROM THE GROUP CONSISTING OF TAR AND PITCH WITH STRONGSULPHURIC ACID BY FORMING AN INTIMATE MIXTURE CONSISTING OF SAID BINDERAND SAID ACID, IN AMOUNT FROM 2% TO 25% BY WEIGHT OF SAID BINDER,ADMIXING SAID ACID TREATED BINDER WITH A TITANIUM OXIDE BEARING MATERIALAND A CARBONACEOUS REDUCING AGENT AND FORMING SAID ADMIXTURE INTOBRIQUETTES ADAPTED FOR CHLORINATION.